The use of solid lubricant additives in gear oils as antiwear and extreme pressure agents is well known to those in the lubrication field. These solids lubricant additives have been added to the gear oil as a stable dispersion and it is desireable that they remain stable in order for these benefits to be realized. When gear oils containing conventionally dispersed solid lubricants are used in gear systems which are exposed to water contamination, the gear oil tends to completely emulsify the water holding it in the oil. This condition is highly undesireable because it predisposes the gears to corrosive pitting and other ramifications of improper lubrication. In conventional gear oils, the removal of the emulsified water from the oils is accomplished by adding special demulsification agents to the oil. Demulsification is the separation of water droplets from a gear oil to form a separate and distinct layer or phase which can be removed from the gear box. In the case of lubricants which contain dispersed solid lubricant additives, the incorporation of such demulsification agents frequently results in flocculation of the solid particles. The flocculation of the solid lubricant particles causes them to separate from the oil by settling thus removing the additive from the oil; the benefits gained from the incorporation of solid particles in the oil are thus lost.
Therefore there is a need in the field for a solid lubricant additive, which, when incorporated in a gear oil used in water contaminated environments, would allow the lubricating solids to remain dispersed in the oil and impart the known benefits of lubricating solids and provide for the removal of emulsified water.
The object of the present invention is to provide a solid lubricant additive for gear oils. The unique character of this additive is that it not only exhibits outstanding dispersion quality, but also has the demulsibility characteristics required for field use and retains the outstanding dispersion quality even in the presence of water contamination.
The use of solid lubricant additives is known in the art.
U.S. Pat. No. 3,384,581, issued May 21, 1968, discloses a composition comprising a particulate material dispersed in a fluid organic material and contained a stabilizing agent. The stabilizing agent disclosed is an ethylene-propylene copolymer or terpolymer. The solid lubricant additive disclosed in this patent was intended to provide enhanced stability of the particulate material at elevated temperatures.
U.S. Pat. No. 3,384,580, issued May 21, 1968, discloses a stabilized dispersion comprised of graphite dispersed in a fluid organic carrier material and contains a stabilizing agent for dispersing the graphite throughout the mixture. The stabilizing agent which is utilized is an ethylene-propylene copolymer or terpolymer and was used to give better high temperature stability to the dispersed graphite.
U.S. Pat. No. 3,062,741, issued Nov. 6, 1962, discloses an improved molybdenum disulfide lubricant in particulate for and a method for making the same and to dispersions containing such improved lubricants. The invention comprises molybdenum disulfide particles having a mass mean diameter of about 0.45 microns to about 2 microns and at least 99.9 percent by weight of the particles having a diameter of less than 32 microns.
U.S. Pat. No. 3,156,420, issued Nov. 10, 1964, discloses an improved molybdenum disulfide lubricant in particulate form, a method of making this lubricant and dispersions containing such improved lubricants. The invention further comprises a method for making finely divided molybdenum disulfide which comprises the steps of grinding molybdenum disulfide in the presence of a compatible grinding aid selected from the group consisting of salicyclic acid and phthalic anhydride.
U.S. Pat. No. 3,842,009, issued Oct. 15, 1974, discloses a liquid lubricant composition comprising a homogeneous stable suspension of finely particulated molybdenum disulfide in a base oil incorporating a dispersant. The dispersant comprises a specific copolymer of methacrylate ester and n-vinyl pyrrolidone. These elements are present in controlled proportions relative to the quantity of molybdenum disulfide present.
U.S. Pat. No. 4,417,991, issued Nov. 29, 1983, discloses a graphite automotive gear oil containing extreme pressure additives. The presence of the extreme pressure agents in the gear oil created a tendency of the oil composition to thicken in use. The use of a dispersant consisting of an ethylene-propylene copolymer grafted with a nitrogen containing vinyl functionality selected from the group consisting of an n-vinyl pyrrollidone and an n-vinyl pyridine.
U.S. Pat. No. 4,136,040, issued Jan. 23, 1979, discloses an improved lubricating oil composition comprising an oil of lubricating viscosity, a minor amount by weight of solid particles to effect improved lubricating properties of the composition, and a minor amount of a nitrogen-containing mixed ester of a carboxy-containing interpolymer. Generally, a nitrogen containing mixed ester of a carboxy containing interpolymer is a polymer which has a reduced specific viscosity in the range from about 0.05 to about 2, and is characterized by the presence of at least one of each of three pendant polar groups within its polymeric structure: (A) a high molecular weight carboxylic ester group which has at least eight (8) aliphatic carbon atoms in the ester radical; (B) a low molecular weight carboxylic ester group with no more than seven (7) aliphatic carbon atoms in the ester radical; and (C) a select carbonyl-polyamino group. This composition provides improved inhibition of sludge and varnish formation in use in engine oils.
U.S. Pat. No. 4,411,804, issued Oct. 25, 1983, discloses an improved lubricating oil composition comprising an oil of lubricating viscosity, a small amount by weight of solid lubricating particles, and a minor amount of certain dispersant-VI improvers. Generally, the solid particles were selected from the group consisting of graphite, molybdenum disulfide, zinc oxide, and mixtures thereof. This composition was intended to provide improved inhibition of sludge and varnish formation in automotive engine use.
U.S. Pat. No. 4,434,064, issued Feb. 28, 1984, discloses a method for stabilizing a graphite in oil dispersion by means of a fracture induced oxidation of graphite particles. The oxidized graphite particles produce a composition suitable as a constituent of the lubricating oil composition. The oxygen content of the graphite particles is at least about one percent by weight of the total weight of the ground graphite particles included in oxygen.
Thus, the art has recognized that solid lubricant additives incorporated in conventional lubricants give the lubricant enhanced anti-wear properties, load carrying capacity, and can also decrease energy consumption. However, it has been surprisingly discovered that the addition of a solid lubricant additive, comprised of a solid lubricant in the presence of an ethylene-propylene copolymer and organic fluid carrier, to a gear oil exhibits excellent dispersion of the solid particles and outstanding water demulsibility characteristics. The additive is generally intended for use in water contaminated environments or in environments in which the potential of water contamination exists.